1. Filed of Invention
Strong-motion accelerographs are often installed in major structures to record earthquake shocks which they may receive. Battery-powered instruments require periodic maintenance, and their records are subject to destruction by heat. For better overall reliability in sensitive locations, such as power and chemical plants, additional instruments are often installed of a type which requires no external power nor recording tape, film, or paper, but employs passive resonant seismic elements which make stylus traces or "scratches" on metallic record plates. From the peak excursions of a series of traces made with elements or units of different natural frequencies, it is possible to reconstruct the shock response spectrum. An instrument of this type is described in my prior U.S. Pat. No. 3,740,757. That instrument employs an array of, typically, twelve resonant reeds, each carrying a stylus, having natural frequencies ranging from about 2 Hz to 25.4 Hz.
A need has arisen for an instrument of this general type that is somewhat more compact and contains more recording channels covering a wider range of natural frequencies, with constant sensitivity per channel. The instrument of the above prior patent cannot be merely adapted to do this; a new approach is required.
2. Prior Art
The closest prior art of which I am aware is in the following U.S. Patent Nos:
(a) Engdahl 3,683,397 PA1 (b) Engdahl 3,740,757 PA1 (c) Engdahl 3,795,006 PA1 (d) Cohen 3,800,921 PA1 (e) Engdahl 3,974,504 PA1 (f) Engdahl 4,100,807
Patents (a)-(c) show the basic recording principle used here, with (a) and (b) showing arrays of resonant reeds of graduated natural frequencies. Reference (d) shows an air dashpot damper; (e) shows a magnifier-type recording unit using the "platform" mechanism which is also used herein; (f) shows another reedtype unit.